In a tubular body to be used as a rotating member in various machines, it is sometimes required to measure the precision of the shape. For example, in a substrate of a photosensitive drum for use in electrophotographic systems such as copying machines, a tubular body after the tube manufacturing steps is subjected to a shape measuring to keep high precision of the shape.
As a method for measuring the shape, there is a method shown in FIGS. 56 and 57. In this method, in a state in which the external peripheral surface 12 of portions near both ends of the tubular body 90 are supported by reference rollers 91, displacement measuring devices 92 are brought into contact with three positions on the longitudinal central portion of the external peripheral surface of the tubular body 10. Then, the tubular body 10 is rotated by rotating the reference rollers 91 to obtain the variation of the detected values of the displacement measuring devices 92. Using the detected values, the displacement at the longitudinal central portions of the external peripheral surface of the tubular body 10 is measured. Such obtained displacement reflects the deflection of the central external peripheral surface with respect t the external peripheral surfaces of the longitudinal end portions of the tubular body 10.
In cases where the tubular body 10 is rotatably supported at the inner peripheral surfaces of the end portions, the thickness distribution (unevenness of thickness) of the tubular body 10 affects the accuracy of rotation. Accordingly, in cases where high precision of shape is required, it can be considered that it is evaluated taking account of the degree of unevenness of thickness by measuring the maximum thickness and the minimum thickness of the tubular body 10.
However, the method for measuring the shape of the tubular body using the deflection measurement of the external peripheral surface of the tubular body 10 shown in FIGS. 56 and 57 and the thickness measurement using thickness measuring devices has the following problems.
(1) Since the deflection measurement of the external peripheral surface and the thickness measurement are performed by using different measuring devices, device differences among the measuring devices, errors arose from the handling of measuring devices and dispersion of the measuring persons will accumulate, which makes it difficult to attain high accuracy of measurement.
(2) Although the deflection of the external peripheral surface and the distribution of the thickness may sometimes be set off geometrically, both of them are measured separately. Therefore, the aforementioned circumstances cannot be considered. As a result, there is a possibility that excessive quality is requested.
Japanese Unexamined Laid-open Patent Publication Nos. H11-271008, S63-131018, 2001-336920, H8-141643, H11-63955, H3-113114, 2000-292161 and H2-275305 for example, disclose various techniques for measuring a shape of a tubular body. However, these publications fail to disclose techniques capable of measuring deflection of an external peripheral surface of a tubular body easily with high precision.
Furthermore, it can be considered to employ a method for measuring a shape of a tubular body using a conventional circularity measuring device. In this case, however, it is required to repeatedly perform every tubular element such that the rotating axis of a measurement table on which the tubular body is disposed and the central axial position of the tubular body to be measured are aligned and that the rotating axis of the measurement table and the central axis of the tubular body are aligned in parallel, which takes a lot of time and trouble.